As a specific example for a valve device that controls a flow rate, a conventional technology will be described using an exhaust gas recirculation (EGR) valve (see, e.g., JP2009-002325A). The EGR valve that operates a valve by an actuator includes an opening degree sensor (e.g., angle sensor) as a means for detecting an operation condition (valve opening degree) of the valve by the actuator.
An opening degree sensor provided for the EGR valve is set to produce a “predetermined sensor output” at the time of “a predetermined valve opening degree”. To describe an example for assisting the understanding, writing to a memory is carried out to produce the sensor output of 1.2 V when the valve opening degree is fully closed, and the sensor output of 4.0 V when the valve opening degree is fully open, in a production process of the EGR valve. Accordingly, the mechanical “valve opening degree” of the EGR valve and the electrical “sensor output” outputted by the opening degree sensor correspond to each other.
Issues of the conventional technology will be discussed. There is a request to “temporarily” open-control the EGR valve for flow rate adjustment. In recent years, there is a request to “constantly” open-control the EGR valve for flow rate adjustment. In this case (at the time of open-control), the flow rate adjustment is made based on the sensor output from the opening degree sensor, so that a “flow rate obtained from the sensor output (referred to as an operation flow rate)” and an “actual flow rate through the EGR valve (referred to as an actual flow rate)” may correspond to each other.
However, despite the correspondence between the “valve opening degree” and the “sensor output”, a flow rate error (deviation of the increase and decrease of the flow rate common to the EGR valves) may be caused due to, for example, the variation (production error) in shape of a component that constitutes the EGR valve. As a result, the “operation flow rate obtained from the sensor output” and the “actual flow rate through the EGR valve” may not correspond to each other. Thus, even though the EGR valve produced by the conventional technology is open-controlled, the flow rate of EGR gas cannot be controlled with high precision.
Although the “issues of the conventional technology” have been described above using the EGR valve, they are not the issues caused only for the EGR valve. Another valve device, such as a valve disposed in a throttle valve or turbocharger, also causes similar issues at the time of open-control.